250 



Sir James Dewar 



[Jan. 16, 



J ^ the C f h T» greened for the first measurement, 

 while for the second a plate of known thickness (down to a fraction 

 ol a mm.) of the material to be examined was placed on a li^ht stage 



above the membrane. Usually two sets of observations were made 



,-! n c <i Cube ' ° ne at room ^mperature and the other at 



100 U - borne lower temperatures were tried with interesting- results. 



ine working arrangement is shown in Fig. 4. Details of the 



